1. Field of the Invention
The present invention is used in the field of medicine, and more particularly, can be used in ophthalmology as an intraocular lens for replacement of a cataract impaired natural lens.
2. Description of the Prior Art
The natural lens of the eye is often impaired by cataracts, particularly in older patients. Cataracts cloud the lens, increasing the opacity of the lens and thereby blurring or reducing the quality and clarity of the image provided to the retina by the lens. In extreme cases, the ability to distinguish an image is lost. A remedy which restores vision is available. Removal of the cataract impaired lens and replacement with an implantable artificial lens is an increasingly typical medical procedure for middle aged and elderly patients. A number of materials may be used in forming the artificial replacement lens, commonly known as an intraocular lens. Among these materials are acrylics, silicones, and hydrogels. All of these materials have a refractive index suitable for use as a intraocular lens. Most typically, these implantable intraocular replacement lenses are monofocal lens. Recently, bifocal intraocular lenses have been developed which include a small central region with a fixed second power focus adapted for near vision conditions.
One significant challenge is that an intraocular lens is located in an environment subject to muscular movement or adjustment as the patient changes the focus of viewing between distance viewing and near viewing. In the natural lens, ciliary muscles and fibrils tense in near vision situations to incrementally alter the lens shape slightly and thereby alter the focal length of the natural lens and increase the lens power, moving it forward and thickening or steepening the optical quality to facilitate sharper focus of near objects on the retina. This process is called accommodation. However, it should also be recognized that with aging, there occurs some loss of ability to exert accommodative muscle forces over the entire range of movement of a younger adult. Providing an intraocular lens which mimics the natural accommodation process associated with the ciliary muscles of the eye is an important goal for ophthalmology. One approach has been to supplement the implantable intraocular lens with a mechanical accommodation device which drives a small central portion axially in response to ciliary muscle tensing. Such mechanically driven devices, however, seem extraordinarily complex. For example, Brady et al., Pub. No. US2007/0100444, discloses a mechanically driven accommodating intraocular lens.
An alternative approach, disclosed in U.S. Pat. No. 6,638,305 by Laguette, following Portney U.S. Pat. No. 5,225,858, the entire disclosures of which are both incorporated herein by reference, is to employ an implantable intraocular lens with a relatively rigid outer portion and a relatively highly deformable inner core completely surrounded by the relatively rigid outer portion. The optical properties of the combination lens are altered by peripheral compressive squeezing to reshape the anterior face of the combination lens, thereby changing a first configuration of the combination lens with a single optical power into a second configuration of the combination lens with a plurality of optical powers.
It would be extremely desirable to provide an accommodating intraocular lens for replacement of cataract impaired natural lens, where such an accommodative lens was incrementally responsive to accommodative muscle tension in a manner more elegantly simple and in a manner which is more similar to that of the original unimpaired natural lens. The present invention advances the approach disclosed by Laguette in at least three ways, (1) by providing optical reshaping of both anterior and posterior surfaces by employing a core (i.e., inner lens portion) with a central location and deformable and resilient properties, (2) by accentuating the optical changes resulting from optical reshaping associated with deformation of the core by exposing the core on both anterior and posterior surfaces of the lens where the exposed anterior and posterior surfaces of the core are both optical surfaces of either spherical or aspherical optical shape, and (3) by providing an interface between the outer lens portion and the inner lens portion (i.e., core) which more efficiently drives the deformational reshaping of the core so as to allow aging patients to achieve accommodation in spite of some loss of accommodation force or range.